Types of URLs
There are essentially 3 kinds of URLs available:
1. Fully Qualified URI
A URI is a "Universal Resource Identifier". Using a URI is a sure-fire way of targeting a specific file, without fail. You can use a URI on any page, on any site, in any email, from any computer. It will always work.
2. From the Root (recommended)
These URLs are URI "short-cuts" -- they simply eliminate the HTTP and domain name. They will work on any page that resides on the same domain.
The slash at the beginning of the URL is a replacement for the "root" domain name.
We reccomend using "from the root" URLs because they provide the greatest flexability with regard to security and ease in setting up your pages.More Info
3. Relative (to the HTML page)
Relative URLs are friendly, and easy to write, but can be problematic because they only work for the page that they exist on. If you were to use the same code on another page, chances are the relative URL will not work.
The URL targets a file relative to the HTML page.